Typically such a bearing supports the rotating load with respect to ground. The fixed element is typically a plain bearing or a race, and the moving element has a bearing journal or a race fixed to the moving element, typically by an interference press fit. The weight of the load is taken vertically on the upward facing side of the fixed element, via the rolling elements where provided. The moving element rotates in use, so that the load is transmitted progressively and repeatedly around the entire circumference thereof. However the fixed element which is stationary with respect to ground, has weight taken continuously by the same upwards facing portion; conversely the downwards facing portion takes no weight. As a result wear of the relatively fixed element is asymmetric, and the bearing may require replacement more frequently than if wear had been distributed around the entire circumference of the fixed element.
The problem of asymmetric wear is most apparent in bearings which support sustained unidirectional loads and/or support high bending forces in the vertical plane, such as hub bearings of wind turbines. The traditional solution is to employ larger bearings of high precision, but also to accept that more frequent replacement may be necessary. Large bearings are difficult and expensive to manufacture, and tend also to suffer disproportionate deterioration due to vibration compared with small bearings.
What is required is an arrangement capable of eliminating this kind of asymmetric wear profile, but which is adaptable to standard types of bearing, particularly rolling element bearings, and particularly to the fixed and moving elements which transmit loads via the bearing.
A further problem is sustained static pressurisation of bearing lubricant between the metal surfaces of the bearing. This occurs in the region of the upper side of the fixed race of the bearing arrangement when it is static. Over time, hydrogen atoms may escape from hydrocarbon molecules in the lubricant and react with the metal surfaces resulting in hydrogen embrittlement of the metal surfaces, which increases the incidence of failure.
What is required is an arrangement capable of limiting the exposure of the metal surfaces to prolonged contact with static pressurised lubricant.